Electrically variable pneumatics structural element

ABSTRACT

The internal pressure p 1  of the hollow body of a pneumatic structural element that comprises a hollow body ( 1 ), at least two traction elements ( 4 ) and at least one compression member ( 2 ) can be electrothermally varied by means of a fluid. The hollow body ( 1 ) houses a void ( 12 ) which is filled with a gas ( 15 ), and a container ( 9 ) which contains a volatile liquid ( 10 ). Said liquid ( 10 ) can be heated or cooled by means of a heat pump ( 13 ). Said heat pump ( 13 ) thermally contacts the liquid ( 10 ) via lamellas ( 24 ). A pressure sensor ( 14 ) measures the pressure inside the void ( 12 ). A cable ( 16 ) links the sensor ( 14 ) and the heat pump ( 13 ) with control and regulating electronics ( 23 ).

The present invention relates to a means for changing the operatingparameters of a pneumatic component having the form of an elongated,air-tight hollow body with at least one compression member extendingalong the hollow body on the load-bearing side and at least two strapsstretched about the hollow body in the opposite winding directions. Thestraps start and/or end at node elements which are arranged at the endsof the at least one traction element, and each encircles the hollow bodyat least once.

Such pneumatic components are known per se, for example from Pat. No.01/73245 (D1).

In this case, the pneumatic element includes a flexible, gas-impermeablehollow body, for example with textile cladding. At least one tractionelement is arranged extending along a surface line on the outsidethereof in such manner that it is impossible for it to bend. Two strapsare attached to the ends of this traction element and encircle theessentially tubular hollow body once in opposite winding directions andcross each other at the longitudinal midpoint of the hollow body on asurface line of the hollow body that is opposite that of the tractionelement. The points where the traction element is attached to straps arenodes, to which the bearing forces are also applied. This ensures thatall bending moments except those generated by the service load—and theweight—of the pneumatic component are prevented from being transferredthereto.

The pneumatic component disclosed in D1 has a number of drawbacks, whichbecome apparent in operation: when it is being set up, the component ora combination of several components is loaded with compressed air viaone or more valves and then retains the quantity of compressed air thatwas introduced. The three essential operating parameters of thecomponent, the pressure in the hollow body, the tensile stress in thestraps and the compressive stress in the compression member, are definedby the geometry of the individual parts and by the initially selectedoperating pressure in the hollow body.

Except for the pressure in the hollow bodies, if it is regulated viavalves and pressure lines throughout its operation, the parameters inthe unloaded component are unchanged and cannot be adapted to specificoperating conditions. Pressure regulation via centralised pressuregeneration and distribution to the components is labour-intensive andexpensive. The pressure lines, which must be connected to eachcomponent, may also hinder the rapid and simple setup of largerstructures made from these pneumatic components.

The task of the present invention is to produce pneumatic componentswith tensile and compressive elements, the operating parameters ofwhich, positive pressure in the hollow body, and tensioning of thetensile and compressive elements may be easily varied, controlled andregulated, either separately or together. Such a control devices ishighly advantageous for example in order to equalise variations inpressure caused by temperature fluctuations; it enables a self-actuatingsafety, energy, vibration and shape control of components and convertsthe pneumatic component into an intelligent, adaptive structure that isadaptable in sophisticated manner to changing conditions caused byvarying operating parameters.

The solution to the task is reflected in the characterising part ofclaim 1 with respect to the essential features thereof, and in thesubsequent claims with respect to further advantageous designs.

The object of the invention will be explained in greater detail withreference to the accompanying drawing and on the basis of severalembodiments.

IN THE DRAWING

FIGS. 1 a, b are schematic diagrams of a pneumatic component accordingto the prior art in side view an in an isometric view,

FIGS. 2 a, b are schematic longitudinal and cross sections of a firstembodiment with increased internal pressure of the hollow body,

FIGS. 3 a, b are schematic longitudinal and cross sections of a firstembodiment with reduced internal pressure of the hollow body,

FIGS. 4 a,b,c are schematic diagrams of a second embodiment havingcompression and traction elements of variable length and with passiveand activated actuators,

FIG. 5 is a schematic, longitudinal section of an embodiment of acompression member with integrated piezoelectric stack actuator,

FIG. 6 is a schematic, longitudinal section of an embodiment of atraction element with integrated electrostrictive polymer actuator.

FIGS. 1 a, b are schematic diagrams of an embodiment according to theprior art (D1). FIG. 1 a shows the side view and FIG. 1 b shows theisometric view thereof. The pneumatic component represented includes anelongated, essentially cylindrical hollow body 1, placed under load andwith a length L and a longitudinal axis A, and made from a flexible,air-tight material. A compression member 2 that is loadable with axialforces is attached to the upper side thereof. The ends of thecompression member are designed as nodes 3, to each of which areattached two tensile elements 4. The axial ends of hollow body 1 eachhave a cap 5; one of these caps is equipped for example with a valve 6to allow air into and out of the hollow body.

The two tensile elements 4 encircle hollow body 1 in the manner ofopposite screw threads, each for example at a constant pitch. Therefore,they cross each at a point 8 in the middle of a surface line 7 oppositecompression member 2. Compression member 2 and surface line 7 are bothin the same plane of symmetry E_(s), which also includes thelongitudinal axis of hollow body 1, designated A.

FIG. 2 a shows a cross section through a first embodiment of anelectrothermal, fluid-amplified control device for the internal pressureof hollow body 1, FIG. 2 b shows the longitudinal section. A flexible orelastic, gas-impermeable bladder 12 is installed inside hollow body 1.This bladder 12 includes a container 9 with a volatile liquid 10 (e.g.FCH). Liquid 10 is in equilibrium with its gas phase 15. The choice ofliquid 10 is determined by the operating temperature at which thecomponent will be used. Its boiling point is advantageously in the rangeof its operating temperature. Container 9 is connected to the interiorof bladder 12 via an aperture 11.

In addition, an electric heat pump 13 with reversible heat flow, e.g. aPeltier element is integrated in container 9, one side of the heat pumpbeing in thermal contact with liquid 10, for example via lamellas, andthe other side of which is able to absorb or give off heat externally tobladder 12. Depending on the direction of the heat flow produced by heatpump 13, liquid 10 may be heated or cooled. If liquid 10 is heated andthus caused to evaporate, the transition of liquid 10 from the liquid tothe gas phase results in a several hundredfold expansion of thesubstance, which in an enclosed volume is accompanied by an increase inpressure. When gas 15 is cooled, to below its boiling point, itcondenses, which in turn leads to a reduction in volume and pressure.

At least one pressure sensor 14 is used to measure pressure p₁ thatnormally exists in bladder 12 and container 9 as well as in hollow body1. In order to detect a leak and the associated pressure loss in hollowbody 1, a second leak sensor 14 may be mounted in hollow body 1, butoutside of bladder 12. Many possible designs of such pressure sensorsare known to those with skill in the art, and therefore they will not befurther described here. A cable 16 supplies electrical power to heatpump 13 and passes the measurement signals from the at least onepressure sensor 14 to a programmable controlling and regulating circuit23, which is able to maintain pressure p₁ constant, for example in theevent of temperature variations, or otherwise to modify it.

The increase in pressure in hollow body 1 simultaneously causesincreased tensile stress in traction elements 4 and increasedcompressive stress in compression member 2.

Bladder 12 is designed in such manner and quantity n of liquid 10 iscalculated such that at a maximum temperature T_(max) and a maximumvolume V_(max) bladder 12 is able to sustain the arising pressureP_(1max), which for an ideal gas is (nRT_(max))/V_(max), and gas 15 andliquid 10 cannot escape. To ensure that hollow body 1 does not burst, itis provided for example with a pressure relief valve 25, or it must beensured that hollow body 1 is able to sustain the maximum pressurecreated at maximum temperature T_(max) when heat pump 13 is switched offand not cooling. In order to retard the exchange of heat between theenvironment and the heated or cooled system, including container 9 andbladder 12, and thus to reduce the power required for heat pump 13,bladder 12 may be thermally insulated.

FIGS. 3 a, 3 b show the first embodiment of FIGS. 2 a, b in a conditionin which volatile liquid 10 is almost fully condensed, and bladder 12 isessentially empty, collapsed and limp. Pressure p₂ in hollow body 1 andin bladder 12 is less than pressure p₁. FIG. 3 a shows a cross-sectionalview, and FIG. 3 b shows a longitudinal view thereof.

Similar electrothermal control devices are known for example from Pat.No. WO 01/53902 (D2), in which the pressure differential created by thephase transition is used to open and close a valve.

FIGS. 4 a,b,c show side views of a second embodiment of an electricallyvariable pneumatic component, in which the length and tension oftraction elements 4 and compression member 2 are modifiable. FIG. 4 ashows the second embodiment of an electrically variable component in thepassive condition, meaning that the lengths and stresses in compressionmember 2 and tensile elements 4 are not altered electrically. FIGS. 4 band 4 c are schematic and greatly exaggerated representations of thechange to the component when compression member 2 is lengthened, in FIG.4 b, and when traction elements 4 are shortened, in FIG. 4 c. Control ofthese parts is exercised electrically via electroactive ceramics (EAC)for compression member 2 or electroactive polymers (EAP) for tractionelements 4. The physical effects used are piezoelectricity andelectrostriction. An example of an EAC is lead zirconate titanate (PZT),and example of and EAP is polyvinylidene difluoride (PVDF). Intensiveresearch is being carried out in the field of piezoelectric andelectrostrictive materials and actuators, and a person with skill in theart would be in a position to select a suitable EAC for the compressionmember and EAP for the traction elements, and to stack, bundle, possiblyprestress and combine them in composite structures with other materials.

The advantage of the electric actuators described in the foregoing overelectromagnetic actuators lies in the fact that they do not have anymoving parts and therefore very few signs of wear occur. The materialitself is deformable. In order to obtain a return signal to theregulating circuit regarding the degree of stress in compression member2 or traction elements 4, compression member 2 and traction elements 4are provided with sensors in addition to the actuators. These may beresistance measurement strips, elongation measurement strips, or otherelectrical length or stress sensors, or intelligent actuators may beused. These are made from a material that behaves both as actuator andsensor at the same time, which in principle is true of all piezoelectricmaterials.

Compression members with for example EAC stack actuators and straps withe.g. aramide-clad PVDF actuator bundles in the nature of artificialmuscles currently enable relative length changes in the percent range,and the tension generated is nowadays in the range from 50 to 100 mPa.Compared to the relatively large pressure changes that are achieved inhollow body 1 using electrothermal, fluid-amplified actuators, thevariation capabilities in compression member 2 and traction elements 4are smaller. The response time before the pressure changes in hollowbody 1 is relatively long and the pressure regulation is accordinglysluggish, whereas electroactive actuators are able to respond veryquickly.

This opens up different application possibilities for the differentcontrol devices. The purpose of pressure control is to maintain aconstant pressure and therewith constant tension of the component. Thismay be assured by an adaptation whose response time is measurable inminutes.

Pressure variations due to fluctuations in temperature over the courseof a day or due to the heat of the sun may be compensated in this way.

By contrast, electroactive tension control of the compression member andtensile elements is suitable for damping vibrations and particularlyalso for monitoring the component.

In order to damp vibrations in the component caused for example by thewind, the actuators are operated for example in paraphase to theelectric signal of the sensors. With the sensors in the compression andtensile straps, the load condition of the component may be determinedprecisely.

Malfunctions or conditions approaching operational limits may berecorded immediately. It is also conceivable to combine suchelectrically variable components to form a sound-receptive structurewhen the sensor is used or a sound emitting structure with the actuatoris used.

To enable longer adjustment travel for the change of length in thecompression member and the traction elements, the use of piezoelectriclinear motors is conceivable, and is in keeping with the inventivethought.

If the compression members 2 in designs including more than one of suchare not altered in identical manner, bending moments may be set up invarious directions.

FIG. 5 shows a possible embodiment of an electrically variablecompression member 2 that is made up in part of a stack actuator 17 madefrom EAC. The length alteration, either longer or shorter depending onpolarisation, of the individual actuator elements 18 accumulate to yieldthe total length alteration of stack actuator 17. A positive andnegative voltage is applied alternatingly to actuator elements 18, sothat opposite electrical fields E are created successively in the axisof compression member 2. The piezoelectric effect causes the actuatorelements 18 to become longer or shorter in the field and axis direction.In addition, for example a piezoelectric or piezoresistive voltagesensor 19 is integrated in compression member 2. A cable 16, assuringboth power supply and data transmission, connects the sensor and theactuator to regulating circuit 23, which monitors, controls or regulatesone or a system of pneumatic components. Such a regulating circuitbelongs to the prior art and therefore will not be explained further.

FIG. 6 shows a longitudinal section through a possible embodiment of atraction element 4 with an integrated electrostrictive multilayeractuator. A plurality of electrostrictive polymer layers 21 on alow-expansion carrier layer 20, e.g. an aramide-reinforced strip, areapplied to a part or the entire length of traction element 4, and areseparated and encapsulated by electrically conductive layers 22.Conductive layers 22 may be subjected successively to positive andnegative voltages, and as a result they generate electrical fields Eperpendicular to traction element 4 in the interposed electrostrictivepolymer layers 21. When a voltage is applied, polymer layers 21 extendin the direction of the electrical field. The cross-sectional area oftensile element 4 increases and its length is shortened in accordancewith the principle preservation of volume.

1. A pneumatic component comprising: an airtight elongated hollow bodymade from flexible material, the hollow body being capable of beingcharged with compressed air; at least one compression member extendingalong a surface line of the hollow body and adjacent thereto forprotection against displacement and bending; at least one pair oftractive elements secured at opposite ends of the at least onecompression member wherein the at least one compression member isfurnished at opposite ends thereof with a node for reciprocal,non-positive attachment of the at least one compression member and theat least one pair of tractive elements for absorbing bearing forces;wherein the at least one pair of tractive elements are arranged so as towind round the hollow body at least once and in opposite directions andcross each other on the surface line of the hollow body opposite to theat least one compression member; and wherein means are integrated forelectrically altering at least one of the operating parameters pressurein the hollow body, length of the compression member, or length of thetractive elements.
 2. The pneumatic component as cited in claim 1,wherein means are integrated for electrically altering pressure p₁ inthe hollow body.
 3. The pneumatic component as cited in claim 2, furthercomprising: a gas-impermeable flexible bladder inside the hollow body,the bladder having a smaller volume than the hollow body; a containerfor holding a volatile liquid, the container being installed inside thebladder; a heat pump having reversible heat flow is adapted to heat orcool the volatile liquid; wherein one side of the heat pump is inthermal contact with the liquid and another side of the heat pump isadapted to absorb or give off heat externally to the bladder; andwherein a change in pressure can be brought about by electrothermalmeans with liquid amplification.
 4. The pneumatic component as cited inclaim 3, wherein at least one electrical gas pressure sensor is locatedinside the bladder.
 5. The pneumatic component as cited in claim 4,wherein the bladder is produced from a flexible, low-expansion material.6. The pneumatic component as cited in claim 4, wherein the bladder ismade from an elastic material.
 7. The pneumatic component as cited inclaim 1, wherein the at least one compression member comprises means foraltering the length thereof electrically.
 8. The pneumatic component ascited in claim 7, wherein the means for altering the length of the atleast one compression member includes at least one actuator based onelectroactive ceramic (EAC).
 9. The pneumatic component as cited inclaim 8, wherein the at least one EAC actuator comprises a stackactuator, wherein the stack actuator comprises a plurality of the EACactuators arranged in series.
 10. The pneumatic component as cited inclaim 1, wherein the tractive element comprises means for altering thelength thereof electrically.
 11. The pneumatic component as cited inclaim 10, wherein the means for altering the length of the tractiveelement includes at least one actuator based on electroactive polymers(EAP).
 12. The pneumatic component as cited in claim 11, wherein the atleast one actuator is made from multilayer EAP.
 13. The pneumaticcomponent as cited in claim 7 wherein the means for altering the lengthof the at least one compression member and a length of a tractiveelement are piezoelectric linear motors.
 14. The pneumatic component ascited in claim 7 wherein at least one sensor is present for measuring achange in length of the at least one compression member and a change inlength of a the tractive element.
 15. The pneumatic component as citedin claim 1 further comprising: an electrical controlling and regulatingcircuit connected to a plurality of sensors and actuators of thecomponent; and wherein the plurality of sensors and actuators help inmonitoring and altering the operating parameters of the component. 16.The pneumatic component as cited in claim 1 wherein means forelectrically altering the pressure p₁ in the hollow body and means forelectrically altering the length of the compression member are presentsimultaneously.
 17. The pneumatic component as cited in claim 1 whereinmeans electrically for altering the pressure p₁ in the hollow body andmeans for electrically altering the length of the tractive elements arepresent simultaneously.
 18. The pneumatic component as cited in claim 2wherein the means for electrically altering the pressure p₁ in thehollow body, means for electrically altering the length of thecompression member, and means for electrically altering the length ofthe tractive elements are present simultaneously.
 19. The pneumaticcomponent as cited in claim 3 wherein the bladder is furnished withthermal insulation.
 20. The pneumatic component as cited claim 3 whereinthe heat pump is a Peltier element.